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This lesson covers the surface treatments and finishes applied to polymers and textiles, as required by AQA GCSE Design and Technology (8552), Section 3.2.9. Understanding these processes is essential for the exam and for justifying finishing choices in your NEA project.
Polymers often do not need surface treatments for protection (they do not rust or rot), but treatments may be applied for aesthetics, functionality or branding.
| Method | Description | Example |
|---|---|---|
| Screen printing | Ink is pushed through a mesh screen onto the polymer surface | Printing logos on acrylic panels |
| Pad printing | A silicone pad picks up ink from an etched plate and transfers it to a curved or irregular surface | Printing on pens, golf balls, bottle caps |
| Digital printing (UV inkjet) | A digital printer applies UV-cured ink directly to the polymer | Custom phone cases, signage panels |
| In-mould labelling | A pre-printed label is placed inside the mould before injection moulding; it fuses with the product | Yoghurt pots, margarine tubs, ice cream containers |
AQA Exam Tip: In-mould labelling is an efficient industrial process because the decoration and moulding happen in one operation, reducing manufacturing steps and cost. This is a good example to cite in a question about efficient manufacturing.
Many polymer products are self-finished — the moulding process itself creates the final surface. Injection-moulded products, for example, have a smooth, glossy surface straight from the mould. The mould itself can be textured to give a matt or patterned finish (e.g. the textured back of a TV remote).
Textiles require a wide range of treatments to add colour, pattern, texture and functional properties.
Dyeing is the process of adding colour to textile fibres, yarns or fabrics using dyes dissolved in water.
| Dyeing Method | Stage | Description |
|---|---|---|
| Fibre dyeing | Before spinning | Loose fibres are dyed before being spun into yarn — produces even colour |
| Yarn dyeing | Before weaving/knitting | Yarns are dyed, then woven to create patterns (e.g. tartan, gingham) |
| Piece dyeing | After weaving/knitting | Whole fabric is dyed a single colour — cheapest method |
| Garment dyeing | After construction | Finished garments are dyed — allows late colour decisions |
| Dye Type | Suitable Fibres | Method |
|---|---|---|
| Reactive dyes | Cotton, linen (cellulose fibres) | Form a chemical bond with the fibre; excellent wash fastness |
| Acid dyes | Wool, silk (protein fibres), nylon | Applied in acidic solution; bright colours |
| Disperse dyes | Polyester, acetate | Applied at high temperature and pressure |
| Natural dyes | Most fibres (with mordant) | Extracted from plants, insects, minerals (e.g. indigo, cochineal) |
Batik is a resist-dyeing technique where hot wax is applied to fabric in a pattern. The waxed areas resist the dye, creating a design. After dyeing, the wax is removed by boiling or ironing between newspaper. Batik produces distinctive crackle effects where dye seeps through cracks in the wax.
AQA Exam Tip: Batik is a common exam topic. Be ready to describe the step-by-step process: apply wax → dye the fabric → remove wax. Explain that the wax acts as a resist, preventing dye from reaching the covered areas.
| Method | Description | Scale |
|---|---|---|
| Screen printing | Ink is pushed through a mesh screen onto fabric; one screen per colour | Medium to mass |
| Block printing | A carved block is dipped in ink and stamped onto fabric | One-off / craft |
| Digital inkjet printing | A large-format printer applies ink directly to fabric from a digital file | One-off to medium batch |
| Sublimation printing | Dye is transferred from paper to polyester using heat and pressure | One-off to medium batch |
| Transfer printing | A design is printed on paper, then ironed or heat-pressed onto fabric | One-off to medium batch |
| Discharge printing | Bleach or chemical paste removes colour from dyed fabric in a pattern | Decorative effect |
| Roller printing (rotary) | Engraved metal rollers apply different colours to fabric at high speed | Mass production |
Laminating and coating add functional properties to textiles, such as waterproofing, flame resistance or thermal insulation.
| Process | Description | Example Product |
|---|---|---|
| Laminating | Bonding two or more layers of fabric together (or fabric + membrane) using heat, adhesive or pressure | Gore-Tex jackets (three-layer laminate: outer fabric + PTFE membrane + inner lining) |
| PVC coating | Applying a layer of PVC to fabric | Tablecloths, raincoats, bags |
| Wax coating | Applying wax to cotton fabric | Barbour jackets, canvas bags |
| Teflon coating | Applying a PTFE-based finish | Stain-resistant school uniforms, tablecloths |
| Silicone coating | Applying a silicone layer to fabric | Waterproof tent fabric, umbrella canopies |
| Finish | Purpose | How It Works |
|---|---|---|
| Mercerising | Improves lustre, strength and dye uptake of cotton | Cotton is treated with sodium hydroxide under tension |
| Calendering | Creates a smooth, shiny surface | Fabric is passed through heated rollers under pressure |
| Sanforising | Prevents shrinkage | Fabric is mechanically compressed to pre-shrink it |
| Brushing/raising | Creates a soft, warm nap | Wire-covered rollers raise fibres from the fabric surface |
| Flame retardant treatment | Reduces flammability | Chemical treatment (e.g. Proban) — required for children's nightwear |
| Anti-bacterial finish | Prevents odour and bacterial growth | Silver-ion or chemical treatment — used in sportswear and medical textiles |
AQA Exam Tip: Functional finishes are often tested. Know at least three examples and link each to a real product. For example: "Flame retardant treatment is applied to children's nightwear to meet British safety standards BS 5722."
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